The invention relates to a piston pump as defined hereinafter.
The piston pump is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR and EHB are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR or FDR or EHB). In a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (FDR) and/or an electrohydraulic brake system (EHB), the pump is needed. With the wheel slip control (ABS or ASR), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (ASR) can for instance be prevented. In a brake system serving as a steering aid (FDR), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from braking out of the lane desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.
Many such piston pumps are known. One example that can be named is the piston pump known from German Patent Disclosure DE 41 07 979 A1.
The known piston pump has a rodlike piston, which is displaceably guided axially in a bush. For driving the piston to execute a reciprocating stroke motion, an eccentric element drivable to rotate by an electric motor is used, which acts upon the piston on a face end protruding out of the bush. The bush is inserted into a cylinder bore of a pump housing.
For assembling the known piston pump, its piston is introduced into the bush, and the bush is then screwed into the cylinder bore. The assembly often proves to be difficult, since the piston is not retained in the bush until after the bush has been inserted into the pump housing. This makes assembly more difficult, especially in the case of piston pumps that have a piston restoring spring that forces the piston out of the bush. A further hindrance to assembly in many such piston pumps, which are intended as pumps in hydraulic vehicle brake systems, is that a check valve is mounted as an inlet or outlet valve on the piston, so that even more individual parts have to be put together that gain a secure hold only after the bush together with the piston is inserted into the cylinder bore of the pump housing.